Driver circuits in lighting devices are used to drive current through a light, such as a compact fluorescent (CFL) tube. In particular, the driver circuit receives an input voltage and outputs an appropriate voltage for the light. For example, a driver circuit may receive a line voltage of 120 Volts at 60 Hertz and output a voltage of approximately 80 Volts at several kilohertz for a CFL tube, or other parameters as required by the specific light. Self-oscillating resonators (SOR) may be used to generate the output voltage of the driver circuit.
FIG. 1 is a circuit illustrating a conventional self-oscillating half-bridge driver for compact fluorescent (CFL) tubes. A circuit 100 includes a start-up stage 102, including a DIAC 104. The circuit 100 also includes a half-bridge self-oscillating resonator stage 112, including transistors 112A and 112B. The circuit 100 further includes a load stage 132, including a CFL bulb 134. An RC timer, including the resistor Rstart and the capacitor C2, along with the DIAC 104 act to start-up the self-oscillating resonator stage 112 by injecting current into a base of the transistor 112B to start oscillation. A transformer 114 couples the load stage 132 to the transistors 112A and 112B to provide feedback and allow self-oscillation in the stage 112. Thus, the self-oscillating resonator stage 112 acts as a power converter for converting power from a line input voltage to a voltage appropriate for the CFL bulb 134.
However, the circuit 100 of FIG. 1 may not be optimal for use with certain loads, such as light emitting diodes (LEDs). Additionally, the circuit 100 of FIG. 1 provides no control over the power conversion and thus no control over the output of the CFL bulb 134. For example, there is no dimming capability in the circuit 100 of FIG. 1.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved lighting systems, particularly for consumer-level devices. Embodiments described here address certain shortcomings but not necessarily each and every one described here or known in the art.